One way to fasten the metallic commutator segments to the insulating body of the commutator is to provide these segments as inserts in a molded plastic commutator body. However, this molding process requires precise and time-consuming positioning of the commutator segments and the resultant molder commutators have to be individually hand finished to remove the inevitable unwanted excessive pieces of plastic material.
To avoid this difficulty, the commutator body and the commutator segments are formed separately so as to cooperate with each other and are subsequently assembled in a manner which ensures that the segments are securely fastened to the commutator body.
Thus, as disclosed in the specification of UK Patent No. 2 105 527, it is known to provide a commutator comprising an insulating commutator body having a cylindrical outer surface and integral, radially extending axial support means formed with axially extending openings; at least three commutator segments mounted on the body, each having an arcuate brush contacting portion seated on the cylindrical outer surface of the body, radial positioning means extending axially from one end of the brush contacting portion into one of said axially extending openings, and a radial terminal stem; and an insulating clamping member for clamping the radial terminal stems between the axial support means and the insulating clamping member.
In this known construction, the radial terminal stem of each commutator segment extends radially from one end of the arcuate portion of the segment forming the brush contacting portion and the radial positioning means consist of two axial projections on opposite sides of the radial terminal stem. The clamping member is an annular ring which is press-fitted over the brush contacting portions of the commutator segments so as to clamp the radial stem portions against the axial support means. As a result, difficulty is encountered in fitting the clamping member. The two radial positioning means are also of limited effectiveness in that the proportion of the circumferential width of each segment available for use in the radial positioning means is limited because the central part, between the radial positioning means, is used to form the radial terminal stems. Moreover, when the segments are secured in position by the clamping member, the radial loading on the segments is provided solely, or almost solely, by the clamping member.